Pressure-induced frustration in charge ordered spinel AlV₂O

AlV2O4 is the only spinel compound so far known that exists in the charge ordered state at room temperature. It is known to transform to a charge frustrated cubic spinel structure above 427 ° C. The presence of multivalent V ions in the pyrochlore lattice of the cubic spinel phase brings about the charge frustration that is relieved in the room temperature rhombohedral phase by the clustering of vanadium into a heptamer molecular unit along with a lone V atom. The present work is the first demonstration of pressure-induced frustration in the charge ordered state of AlV2O4. Synchrotron powder x-ray diffraction studies carried out at room temperature on AlV2O4 subjected to high pressure in a diamond anvil cell show that the charge ordered rhombohedral phase becomes unstable under the application of pressure and transforms to the frustrated cubic spinel structure. The frustration is found to be present even after pressure recovery. The possible role of pressure on vanadium t2g orbitals in understanding these observations is discussed.